Glass article with metal member joined thereto, and junction structure using the same

ABSTRACT

The present invention is intended to provide a glass article with a metal member joined thereto in which an electroconductive coating film is formed on at least a part of the surface of the glass article by baking a silver paste that includes Ag particles and a glass frit, a joining plane of the metal member is fixed onto the electroconductive coating film with a lead-free solder alloy containing Sn as a main component, and the lead-free solder alloy contains at least 1.5 mass % of Ag, which prevents the appearance of the electroconductive coating film and the bonding strength from degrading. Furthermore, in the present invention, when using a metal member having at least two joining planes, the total area of the joining planes is set within a range of 37 mm 2  to 50 mm 2 , which allows high bonding strength between the glass article and metal member to be maintained while using the lead-free solder alloy. Moreover, in the present invention, the volume of the lead-free solder alloy to be provided on each joining plane is set to be 1.0 to 2.0 times the product of the area of the joining plane concerned and the thickness of the lead-free solder alloy, which prevents cracks from occurring in the glass article.

TECHNICAL FIELD

The present invention relates to a glass article with a metal memberjoined thereto, and a structure of joining a glass article and a metalmember together. Particularly, the present invention relates to anadequate junction made between a glass article and a metal member usinga lead-free solder alloy.

BACKGROUND ART

In order to ensure the driver's view, electroconductive lines (heatingwires) are formed as a defogger on the surface of a glass sheet to beused for a rear window of a car in some cases. The defogger is suppliedwith an electric current through a feeding metal terminal. This metalterminal is provided on a bus bar connected to the defogger. In somecases, a glass antenna may be used for the rear and side windows of acar. In the case of using the glass antenna, electroconductive lines areformed, on the surface of a glass sheet, in a pattern (an antennapattern) corresponding to the wavelength to be received. A metalterminal also is provided for the feeding point of this antenna pattern.

Generally, the electroconductive line and bus bar are formed by baking asilver (Ag) paste printed onto the surface of the glass sheet. The Agpaste normally contains Ag particles, a glass frit, and a solvent. Ametal terminal is fixed onto the electroconductive coating film formedby baking this Ag paste. Conventionally, a metal terminal is solderedusing a tin-lead (Sn—Pb-based) solder alloy. Recently, from theviewpoint of environmental protection, it has been demanded to use alead-free solder in producing car window glass.

However, when a metal terminal is joined to a glass sheet using alead-free solder alloy, particularly, a Sn-based lead-free alloy, thefollowing problems occur.

First, the electroconductive coating film may melt and flow into thesoldered junction, which may impair the appearance of theelectroconductive coating film. The bond strength also degrades togetherwith the degradation in appearance.

Second, it tends to be more difficult to ensure the bond strength of themetal terminal as compared to the case of using the Sn—Pb-based alloy.This tendency becomes conspicuous when using a metal terminal having aplurality of joining planes.

Third, cracks may occur at the surface of the glass sheet in thevicinity of the soldered junction due to a rapid temperature change.Even if the cracks caused in the glass sheet are minute, they should beavoided when consideration is given to the long term strength of theglass sheet. This phenomenon also becomes conspicuous when using a metalterminal having a plurality of joining planes.

In conjunction with the second problem, for example, JP-U-61(1986)-37182discloses that the bond strength increased with an increase in solderedjoining area.

DISCLOSURE OF THE INVENTION

The first problems can be solved by an addition of Ag to a Sn-basedlead-free solder alloy. The addition of Ag improves not only theappearance but also the bond strength. From a first aspect, the presentinvention provides a glass article with a metal member joined thereto inwhich an electroconductive coating film is formed on at least a part ofthe surface of the glass article by baking a silver paste that includesAg particles and a glass frit. A joining plane of the metal member isfixed onto the electroconductive coating film with a lead-free solderalloy containing Sn as a main component, and the lead-free solder alloycontains at least 1.5 mass % of Ag, for example, 1.5 to 5 mass % of Ag.

In order to solve the second problem, a metal terminal was used that hadan enlarged joining plane, but thereby the bond strength ratherdecreased. Surprisingly, the bond strength was improved by using a metalterminal with a smaller joining plane than conventional one. From thesecond aspect, the present invention provides a glass article with ametal member joined thereto in which an electroconductive coating filmcontaining Ag is formed on at least a part of the surface of the glassarticle. At least two joining planes of the metal member are fixed ontothe electroconductive coating film with a lead-free solder alloycontaining Sn as a main component, and a total area of the at least twojoining planes is in the range of 37 mm² to 50 mm².

The third problem can be relieved not by the increase but the decreasein amount of the solder to be used. When the solder was prevented fromspreading outside the joining plane, less cracks occurred in the glasssheet. From the third aspect, the present invention provides a glassarticle with a metal member joined thereto in which an electroconductivecoating film containing Ag is formed on at least a part of the surfaceof the glass article, at least two joining planes of the metal memberare fixed onto the electroconductive coating film with a lead-freesolder alloy containing Sn as a main component, and with respect to eachof the at least two joining planes, a volume of the lead-free solderalloy is 1.0 to 2.0 times the product of the area of the joining planeconcerned and the thickness of the lead-free solder alloy.

In the present specification, the “main component” denotes a componentthat accounts for at least 50 mass % according to its common use.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a sectional view showing an example of a glass articleaccording to the present invention.

FIG. 2A is a sectional view showing another example of a glass articleaccording to the present invention; FIG. 2B shows a metal terminal ofthe glass article seen from its back side; and FIG. 2C is a plan viewshowing an example of a joining plane with another shape of the metalterminal.

FIG. 3 is a sectional view showing still another example of a glassarticle according to the present invention.

FIG. 4 is a graph showing measurement results obtained in Example 1.

FIG. 5 is a graph showing measurement results obtained in Example 2.

BEST MODE FOR CARRYING OUT THE INVENTION

Since the Sn-based lead-free alloy lacks flexibility as compared to theSn—Pb-based alloy, the junction soldered using this lead-free alloy isinferior in the stress relaxation characteristic. Particularly, whenthere are a plurality of joining planes, thermal stress is developed inthe in-plane direction in the glass sheet by the temperature changecaused by soldering due to the difference in thermal expansioncoefficient between glass and the portion of a metal member thatconnects the joining planes to each other. Accordingly, the strength ofthe glass sheet decreases, and in some cases, cracks may occur at thesurface of the glass that is a brittle material. Actually, it wasconfirmed by a tension test of a metal member (a metal terminal) thatthe terminal and the glass sheet were ruptured due to the breakage notof the junction soldered using the Sn-based lead-free alloy but ratherthe inner portion of the glass in the vicinity of the soldered junction.

Thus, it is considered that the thermal stress has some part in both thedecrease in bond strength and the occurrence of cracks. The former canbe prevented by controlling the joining area within a predeterminedrange, and the latter can be prevented by controlling the amount of thesolder to be used to a degree that does not allow the bond strength todecrease considerably. Specifically, it is preferable that the joiningarea is controlled within the range of 37 mm² to 50 mm², particularly 40mm² to 45 mm². In order to prevent the solder from considerablyspreading outside the joining plane, it is preferable to control thevolume V of the solder alloy to be 1.0 to 2.0 times the product of thearea S of the joining plane and the thickness T of the lead-free solderalloy. In other words, it is preferable to control the volume V so thatthe following relative equation holds:1.0ST≦V≦2.0ST

When the Sn-based lead-free solder alloy containing no Ag is used on anelectroconductive coating film containing Ag that has been formed bybaking a Ag paste, Sn contained in the solder alloy and Ag contained inthe electroconductive coating film form a compound. As a result, theelectroconductive coating film is corroded. In order to prevent theappearance of the glass article from degrading due to this corrosion, aSn—Ag lead-free alloy may be used that contains at least 1.5 mass % ofAg.

Another advantage in adding Ag is that the bond strength increases. Thestrength of the junction soldered using the Sn—Ag alloy increases withan increase in rate of Ag content, but becomes almost constant when therate of Ag content exceeds about 2 wt. %.

On the other hand, an excessively high rate of Ag content causes aconsiderable rise in material cost and also raises the liquidustemperature of the alloy. The increase in liquidus temperature causes anincrease in soldering temperature. Hence, the thermal stress increasesand thereby the workability in soldering also deteriorates. Whenconsideration is given to this, it is preferable that the rate of Agcontent in the Sn—Ag solder alloy is 5 mass % or less, furtherpreferably 4 mass % or less.

With respect to the Sn—Ag alloy, when it has an eutectic composition ofSn-3.5Ag (an alloy made of 3.5 mass % of Ag and Sn that accounts for therest), it has the lowest liquidus temperature (221° C.). In this case,the tip of the soldering iron has a temperature of 310° C. to 320° C. Alow temperature of the tip has an effect of relieving of thermal stresscaused by the difference in thermal expansion coefficient betweenmembers to be joined together. In the Sn-3.5Ag alloy, all the Ag ispresent as an intermetallic compound of Ag₃Sn. In the Sn-3.5Ag alloy,the precipitating grains do not become large as compared to the Sn—Pballoy. This is because Ag atoms do not disperse easily in the solidphase Sn.

As described above, a preferable rate of Ag content in the Sn—Ag alloyis 1.5 to 5 mass %, further preferably 2 to 4 mass %, and particularly 2to 3 mass %. This Sn-based lead-free solder alloy having this rate of Agcontent is particularly suitable for the purpose of joining a metalmember onto the electroconductive coating film formed by baking an Agpaste onto the surface of a glass article. This alloy composition bringspreferable results regardless of whether the number of the joining planeis one or more. The Sn—Ag alloy may contain other minor components. Inthis case, it is preferable that the content of the minor components is0.5 mass % or less.

The metal member having at least two joining planes is not particularlylimited. For example, however, the metal member may be a metal terminalincluding a leg part having the at least two joining planes and aconnection part that projects upward from the leg part and is to beconnected to a cable. Through this metal terminal, electricity can befed to the electroconductive coating film formed on the surface of theglass sheet.

The glass article also is not particularly limited, and for example, aglass sheet may be used that is formed of a soda-lime silicacomposition, as in the conventional case. When it is used for car windowglass, the glass sheet suitably is subjected to tempering, bending, orthe like.

The electroconductive coating film may be at least one selected from anantenna and a defogger. The electroconductive coating film may be formedby printing and baking a silver paste in a predetermined pattern that issuitable for functioning as an antenna and/or a defogger. For the silverpaste, a composition may be used that includes silver particles, a glassfrit, and a solvent, as is conventionally used for glass articles. Itscomposition is not particularly limited, but as an example, it contains70 to 85 mass % of silver particles, 1 to 20 mass % of a glass frit, and5 to 25 mass % of a solvent.

Hereinafter, embodiments of the present invention are described withreference to the drawings.

In a glass article 1 shown in FIG. 1, an electroconductive coating film3 is formed in a predetermined pattern on the surface of a glass sheet2. A metal terminal 5 is joined onto the electroconductive coating film3 with a lead-free solder alloy 4. This terminal 5 has two joiningplanes 5 a and 5 b, a leg part 5 c for bridging these joining planes,and a connection part 5 d that projects upward from the leg part.

In FIG. 1, the lead-free solder alloy 4 spreads slightly toward theelectroconductive coating film 3. The solder alloy 4, however, does notspread out considerably from the joining planes 5 a and 5 b butsubstantially stays between the coating film 3 and the joining planes 5a and 5 b. In order to diminish the spread of the solder alloy 4, forexample, the amount of the solder alloy 4, which is supplied in a stateof being applied onto the joining planes 5 a and 5 b of the terminal,may be limited within an adequate range.

FIG. 1 shows the terminal 5 formed with a metal portion that forms theconnection part 5 d being disposed above a metal portion that forms theleg part 5 c. The shape of the terminal, however, is not limitedthereto. For instance, as shown in FIG. 2A, a terminal 5 may be employedin which a metal portion that forms parts of the connection part 5 d andthe leg part 5 c is combined with a metal portion that forms the rest ofthe connection part 5 d and the leg part 5 c. Such a terminal can beformed with one metal plate being bent.

To the connection part 5 d of this terminal 5 is connected a wire 6having a connector 7 on its end. Through this wire, theelectroconductive coating film 3 is connected electrically to a powersource, an amplifier, etc., which are omitted in the drawing. Asdescribed above, the glass article according to the present invention issuitable for a junction structure in which a cable is connected to theconnection part of the metal fitting and this cable and theelectroconductive coating film are electrically connected to each other,that is, a structure for supplying electricity to the electroconductivecoating film provided on the glass surface.

The shape of the joining planes of the metal terminal is not limited toa rectangle (FIG. 2B) but may be a circle, an ellipse, a semicircle(FIG. 2C), a triangle, a polygon with five vertices or more, or thelike.

As described above, the Sn—Ag alloy of the present invention also can beused for the junction structure with only one joining plane. In thiscase, for example, a planar terminal 9 can be used that has one joiningplane 9 a and a connection part 9 d as shown in FIG. 3.

EXAMPLES Example 1

The same junction structures as that shown in FIG. 1 were produced. Ineach of them, soda-lime silica glass having a thickness of 3.1 mm wasused for the glass sheet 2, a Sn—Ag alloy whose Ag content is shown inTable 1 was used as the lead-free solder alloy 4, and a terminal formedof a Cu metal sheet was used as the metal terminal 5. The areas of thetwo joining planes of the metal terminal 5 are set to be equal (a ratioof 1:1) to each other and to sum up to 56 mm². The electroconductivecoating film 3 was formed by screen-printing an Ag paste containingabout 80 mass % of Ag particles, about 5 mass % of a glass frit, andabout 15 mass % of an organic solvent, drying it, and further baking itat about 700° C.

The lead-free solder alloy was applied to the joining planes of themetal terminal beforehand. The soldering was carried out by applying aflux to the solder alloy, pressing the joining planes of the metalterminal onto the electroconductive coating film, and pressing asoldering iron (with its tip having a temperature of about 310° C.)against the terminal. After the completion of the process, it was leftat room temperature for 24 hours.

With respect to each sample thus obtained, its bond strength wasmeasured. The stress caused when the terminal was pulled upward (FIG. 1)and thereby the terminal and the glass sheet were ruptured, was employedto indicate the bond strength. In addition, the state of a portion ofthe electroconductive coating film located in the vicinity of thejunction was checked visually. The appearance of each sample wasevaluated by comparison with the case of using a Sn—Pb-based solderalloy. The results are shown in Table 1.

TABLE 1 Components Melting Bond (mass %) Temperature Strength Sn Ag (°C.) Appearance (N) Sample 1A The rest 0.5 220-235 D 245 Sample 1B Therest 1.0 220-234 C 333 Sample 1C The rest 1.5 218-231 B 471 Sample 1DThe rest 2.0 219-229 B 529 Sample 1E The rest 2.5 219-228 B 476 Sample1F The rest 3.0 220-225 B 515 Sample 1G The rest 3.5 220-222 B 494Sample 1H The rest 4.0 220-228 B 478 Sample 1I The rest 5.0 220-244 B503 Sample 1J The rest 6.0 220-257 B 457 Sample 1K The rest 7.0 220-268B 482 In each column of the melting temperature, the numbers on the leftand right sides indicate a solidus temperature and a liquidustemperature, respectively. The appearance was evaluated with A standingfor “superior”, B “equivalent”, C “slightly inferior”, and D“considerably inferior”.

In the test of the bond strength, rupture took place inside the glass inall the samples. In the electroconductive coating films of Samples 1Aand 1B, which contain less than 1.5 wt. % of Ag, their appearancesdegraded due to the “silver corrosion phenomenon”.

The relationship between the rate of Ag content and bond strength issummarized and shown in FIG. 4. The bond strength increases until therate of Ag content increases up to around 1.5 to 2 wt. % but becomesalmost constant when it exceeds 2 wt. %.

Except for Samples 1J and 1K, which contain more than 5 wt. % of Ag, thesolder alloys had a liquidus temperature of 250° C. or lower. Inaddition, the respective samples had a solidus temperature of 220° C. orslightly lower. The temperature characteristics (the liquidustemperature: 230° C. or lower, and the difference between the liquidustemperature and the solidus temperature: 10° C. or less) of the samples1D to 1H are advantageous in reducing the thermal stress and shorteningthe cooling time after soldering.

Example 2

Samples were obtained in the same manner as in Example 1 except that aSn—Ag alloy was used that contains 98 mass % of Sn and 2 mass % of Ag,and the total area of the joining planes was set at the values shown inTable 2.

With respect to each sample thus obtained, its bond strength wasmeasured in the same manner as in Example 1. The results are shown inTable 2.

In all the samples, rupture of the junction took place not at thesoldered junction but inside the glass.

TABLE 2 Total Area of Joining Planes Bond Strength Samples (mm²) (N) 2A28 522.3 2B 35 519.5 2C 42 727.9 2D 49 591.8 2E 56 503.1

As is apparent from FIG. 5 showing the relationship between the totalarea of joining planes (joining area) and the bond strength, the bondstrength degrades both in the case where the joining area is too largeand where it is too small. Thus, in order to improve the bond strengthin the junction structure in which the terminal having a plurality ofjoining planes is fixed with a “hard” lead-free solder alloy, thejoining area needs to be designed properly. This proper design alsobrings preferable results from the viewpoint of the reduction in amountof the solder to be used.

Example 3

Samples were obtained in the same manner as in Example 1 except that theamount of the lead-free solder alloy 4 provided on the respectivejoining planes and the total area of the joining planes were set atvalues shown in Table 3. With respect to each of n pieces of samplesthus obtained, a thermal test was carried out through predeterminedtemperature cycling, and the state of the glass surface was checkedvisually every 100 cycles after 200 cycles. The temperature cycling wasset to include a period of retention for 30 minutes at −30° C., a periodof raising temperature to 80° C. in three minutes, a period of retentionin this state for 30 minutes, and a period of decreasing temperature to−30° C. in three minutes, and thus the thermal cycle test was carriedout. The results are shown in Table 3.

In Samples 3A to 3D and 3F to 3G, no cracks occurred in the glass evenwhen the above-mentioned thermal cycle was repeated 500 times. In Sample3A, the bond strength determined by the tension test carried out in thesame manner as in Example 1, however, was lower than that of Sample 3Cby about 25%. On the other hand, since Sample 3G had a reduced joiningarea, its bond strength was higher than that of Sample 3C by about 18%.The volumes shown in the table were calculated from the mass of thesolder alloy and its specific gravity.

TABLE 3 Solder Alloy The number of cracks Amount Volume JoiningThickness V/ caused by thermal test Samples (g) (mm³) Area (mm) ST n 200300 400 500 3A 0.1 13.6 Normal 0.5 0.5 2 0 0 0 0 3B 0.2 27.2 Normal 0.51.0 6 0 0 0 0 3C 0.3 40.8 Normal 0.5 1.5 10 0 0 0 0 3D 0.4 54.3 Normal0.5 1.9 6 0 0 0 0 3E 0.5 67.9 Normal 0.5 2.4 6 3 1 0 1 3F 0.2 27.2Reduced 0.5 1.3 6 0 0 0 0 3G 0.3 40.8 Reduced 0.5 1.9 6 0 0 0 0 3H 0.454.3 Reduced 0.5 2.6 6 0 0 2 1 “Normal” indicates 56 mm², and “Reduced”denotes 42 mm².

INDUSTRIAL APPLICABILITY

As described above, the present invention can provide a glass articleincluding a junction with a metal member that is excellent in strengthwhile using a lead-free solder alloy.

1. A glass article with a metal member joined thereto, comprising: anelectroconductive coating film formed on at least a part of a surface ofthe glass article by baking a silver paste that includes Ag particlesand a glass frit, wherein the metal member comprises two joining planes,a leg part that bridges the two joining planes, and a connection partthat projects unward from the leg part, and wherein the two joiningplanes of the metal member are fixed onto the electroconductive coatingfilm with a lead-free solder alloy containing Sn as a main component,and wherein when the glass article undergoes a tension test in which themetal member is pulled upward, the glass article and the metal memberare ruptured because of a breakage of an inner portion of the glassarticle in a vicinity of a junction portion soldered using the lead-freesolder and not because of a breakage of the junction portion, andwherein the lead-free solder alloy is a Sn—Ag based alloy that contains2 to 4 mass % of Ag, and a content of other minor components except forSn and Ag in the Sn—Ag based alloy is 0.5 mass % or less, and whereinthe Sn—Ag based alloy has a liguidus temperature of 230° C. or lower,and the difference of the liquidus temperature and a solidus temperatureof the Sn—Ag based alloy is 10° C. or less, and wherein a total area ofthe two joining planes is in a range of 40 mm² to 45 mm².
 2. The glassarticle according to claim 1, wherein the electroconductive coating filmis at least one selected from an antenna and a defogger.
 3. The glassarticle according to claim 1, wherein with respect to each of the twojoining planes, a volume of the lead-free solder alloy is 1.0 to 2.0times the product of an area of the joining plane concerned and athickness of the lead-free solder alloy, and wherein the alass articleforms no cracks after 500 times of a thermal cycle, and each thennalcycle consists of a first period of retention for 30 minutes at −30° C.a second period of raisina tenperature to 80° C. in three minutes, athird period of retention for 30 minutes at 80° C. and a fourth periodof decreasing temperature to −30° C. in three minutes.
 4. A junctionstructure, comprising a glass article according to claim 1, wherein acable is connected to a connection part of the metal member, and thecable and the electroconductive coating film are connected electricallyto each other.